The density of semiconductor devices continues to rise, with no end in sight, and the importance of technology for forming multilayer wiring and accompanying interlayer insulation films, or for forming plug, damascene, and other such electrodes becomes much greater as density increases. Naturally, a major concern is the monitoring of the thickness and shape of an interlayer insulation film or metal film (whether or not it is embedded or the like). The monitoring of film thickness is, of course, also necessary in the process of thin film formation or etching, but what has especially been viewed as a problem of late is the detection of the polishing endpoint in a planarization process.
An optical method is employed for such detection of the polishing endpoint. Specifically, the spectral reflectance spectrum at the polishing endpoint is found ahead of time for the wafer or other object of polishing, and when the spectral reflectance spectrum of the object of polishing as observed during polishing approaches the previously found spectral reflectance spectrum, it is concluded that the polishing endpoint has been reached. This method is described, for example, in Japanese Patent No. 3360610 (Patent Document 1).    [Patent Document 1] Japanese Patent No. 3360610